The present invention pertains to a platform for introducing sheet materials, particularly in leather splitting machines and the like.
It is known that splitting machines consist of a band blade disposed around a pair of flywheels, at least one of which is a drive flywheel, provided with axes substantially parallel to each other. The working to be carried out on the sheet material is splitting, that is a longitudinal thinning cut that causes a reduction in the thickness of leather.
In order to achieve this type of working, the material is introduced into the machine in correspondence of the rectilinear sharp portion of the blade from a positioning platform placed in front of said cutting edge. As soon as the cutting operation begins, a pair of feed rollers, disposed close to said rectilinear portion of blade, cause the cut material to move forward.
The conventional platforms for introducing said material consist of a fixed plate mounted on a bearing surface disposed in front of the rectilinear operating portion of the blade. These plates are provided with a very smooth working surface as the material must easily slide thereon, which enables its introduction into the cutting area.
Such an arrangement however, although very expensive, does not ensure a sufficient smoothness when the material to be treated has a high friction coefficient or in any case such a coefficient that a hard sliding is caused.
In these cases in fact when the material is caused to slide along the platform in order to be introduced into the cutting area, it tends to "jib" so that it is brought into contact with the blade under a faulty spreading condition which obviously produces an uneven reduction in the thickness of the leather to be worked.
Still bigger drawbacks occur when workings on leather have to be carried out on dies. It is known that dies are substantially flat patterns having the same shape as the piece to be worked, provided underneath with circumferential and/or central swellings suitable to exert a stronger pressure against the leather situated below so that, after the working, the leather thickness appears more reduced close to the circumferential edge or in the central portions where the above mentioned swellings are present on the die.
It is obvious that on a fixed platform, if hardly sliding materials are concerned, when the material is caused to slide with the die placed thereon in order to introduce it into the cutting area, there is inevitably the occurrence of relative motions between the die and the leather to be worked. Due to these slippings, the machine cannot work correctly, so that the reductions in thickness are not so accurate as it is in some cases required.
In order to obviate these inconveniences, a platform for the introduction of the material has been envisaged, which is provided with a plurality of rollers pivotally mounted on axes parallel to the rectilinear portion of the blade. However, such a platform is, on the one hand, very expensive while, on the other hand, it does not completely solve the problem related to the introduction of leather into the cutting area under a perfect-spreading condition. In fact, the rollers are so shaped that they do not ensure a complete backing for the leather while it is being introduced, so that some portions will always be cut "under measure" and others "over-measure".